AMS1117

UMW · Youtai Semiconductor1 A LDO · UMW

UMW's second-source AMS1117: a positive 1 A low-dropout linear voltage regulator with a typical dropout of 1.2 V at 1 A, in fixed 1.2 / 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V versions or an adjustable version set by two resistors around a 1.25 V reference. Output tolerance is 1.5 % on every fixed version except 1.2 V, which is 2 %. Includes thermal shutdown and current limiting, and takes up to 18 V in. Offered in SOT-223-3L, TO-252-2L and SOT-89-3L.

This page is the UMW / Youtai Semiconductor part only. Everything below comes from the UMW datasheet and applies to UMW-branded silicon. The part number originated at Advanced Monolithic Systems, whose version has a different voltage lineup, a different third package and materially different limits — if your BOM says AMS, use 1 A Low-Dropout Regulator AMS — AMS1117 instead.

Output 1 ADropout 1.30 V max @ 1 AV_IN 18 V max Versions 6 fixed + ADJPackages SOT-223 · TO-252 · SOT-89Pins 3

At a glance

Output current

1 A

Current limit 2.1 A min · 2.5 A max

Dropout

1.30 V max

1.20 V typ at the full 1 A

Fixed outputs

6 versions

1.2 · 1.5 · 1.8 · 2.5 · 3.3 · 5.0 V

Adjustable

1.25 V ref

V_OUT = V_REF(1 + R2/R1) + I_ADJR2

Packages

3 options

SOT-223-3L · TO-252-2L · SOT-89-3L

Input voltage

18 V max

12 V recommended operating maximum

Specifications

Output current1 A

Fixed output voltages1.2 / 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V — also available adjustable

Output accuracy1.5 % on 1.5 / 1.8 / 2.5 / 3.3 / 5.0 V and the adjustable version · 2 % on the 1.2 V version

Reference voltage1.250 V typ — 1.231 – 1.268 V at 25 °C, 1.225 – 1.275 V over the full range

Dropout voltage1.00 typ / 1.20 max at 100 mA · 1.05 / 1.25 at 500 mA · 1.20 / 1.30 at 1 A

Input voltage18 V absolute maximum · 12 V recommended operating maximum

Line regulation9 mV typ, 18 mV max (V_IN(min) ≤ V_IN ≤ 12 V, I_OUT = 10 mA)

Load regulation10 mV typ, 18 mV max (10 mA ≤ I_OUT ≤ 1 A)

Current limit2.1 A min, 2.5 A max

Quiescent current5 mA typ, 10 mA max (4.25 V ≤ V_IN ≤ 6.5 V)

Ripple rejection60 dB min, 75 dB typ (120 Hz, V_IN − V_OUT = 3 V, 1 V_PP ripple)

Adjust pin current60 µA typ, 120 µA max · change 0.2 µA typ, 5 µA max

Output temperature stability0.3 % typ

Temperature stability0.5 % typ

Long term stability0.3 % typ (1000 h at 125 °C)

RMS output noise0.003 % of V_OUT (10 Hz – 10 kHz)

ProtectionCurrent limiting + thermal shutdown at 150 °C typ

Thermal resistance R_θJASOT-223-3L 88 °C/W · TO-252-2L 86 °C/W · SOT-89-3L 102 °C/W

ESD tolerance2000 V minimum

Operating junction temp−40 to +125 °C recommended · 150 °C absolute maximum

Storage temperature−65 to +150 °C

SolderingLead temperature 260 °C, 5 s

Required output cap22 µF tantalum covers all cases; smaller values work without adjust-pin bypassing

Symbol & footprint

Schematic symbol — hover a pin for its function

PCB footprint — switch package bottom-right (SOT-223 / TO-252 / SOT-89)

Pin map — 3 terminals, identical across all three packages

The pinout is the same on SOT-223-3L, TO-252-2L and SOT-89-3L, and on all three the metal tab is V_OUT, internally bonded to pin 2. It is the heat path, so it must be soldered to a copper pour on the output net, never to ground. All three footprints shipped here carry the tab as pad 2.

All packages3 + tab

1	GND/ADJ	Ground on fixed versions; adjust (feedback) node on the adjustable version
2	VOUT	Regulated output — also the metal tab
3	VIN	Input supply voltage, 18 V max
—	TAB	Thermal pad, bonded to pin 2 (V_OUT)

Topside marking3

	SOT-223-3L	`AMS1117` / `3.3` + lot code
	TO-252-2L	`1117 CD` / `3.3` + lot code
	SOT-89-3L	`STK17` / `3.3` + lot code — note the different prefix

Internal structure

The pass element is a single NPN transistor driven by a PNP, so dropout is set by V_DROP = V_BE + V_SAT — which is why this family cannot get below about 1 V and why dropout rises with load. Fixed and adjustable versions are the same die: an on-chip link selection (F1 and F2 connected with A open for fixed, A connected with F1 and F2 open for adjustable) either wires the internal divider to the output or brings the feedback node out on pin 1.

Component variants

All variants are the same silicon. The order code carries the package and the output voltage independently. Unlike the AMS original, UMW spells the adjustable version out as -ADJ rather than leaving the suffix blank.

AMS1117CD-3.3S

AMS1117

base part — 1 A LDO

CD / blank

CD = TO-252-2L · blank = SOT-223-3L

-3.3 / -ADJ

fixed output voltage, or -ADJ for the adjustable version

trailing S selects SOT-89-3L

SOT-223-3Lno letter

5.90–6.70 × 3.90 ±0.30 mm body, 1.60 ±0.15 mm height · 2.30 mm TYP lead pitch · 4.60 ±0.15 mm lead span · tab = V_OUT

Fixed: AMS1117-1.2 -1.5 -1.8 -2.5 -3.3 -5.0

Adjustable: AMS1117-ADJ

R_θJA 88 °C/W

TO-252-2L `CD`

6.40–6.70 × 6.00–6.30 mm body, 2.20–2.30 mm height · 2.20–2.40 mm lead pitch · tab = V_OUT

Fixed: AMS1117CD-1.2 -1.5 -1.8 -2.5 -3.3 -5.0

Adjustable: AMS1117CD-ADJ

R_θJA 86 °C/W — the best thermal option

SOT-89-3L `S`

4.50 ±0.30 × 2.45 ±0.30 mm body, 1.50 ±0.20 mm thick · 3.00 mm BSC lead pitch · tab = V_OUT

Fixed: AMS1117-1.2S -1.5S -1.8S -2.5S -3.3S -5.0S

Adjustable: AMS1117-ADJS

R_θJA 102 °C/W · smallest footprint, marked STK17

The AMS original offers an 8-lead SOIC in place of SOT-89, and a 2.85 V version that UMW does not carry. See the AMS page.

Output voltage versions

Two limit sets per version: the tighter one at T_J = 25 °C with I_OUT = 10 mA, and the wider one over the full load and line range (0 or 10 mA ≤ I_OUT ≤ 1 A).

Version	V_OUT typ	Min – max at 25 °C	Min – max, full range	Test V_IN	Accuracy
AMS1117-1.2	1.200 V	1.176 – 1.224 V	1.152 – 1.248 V	3.2 V	2 %
AMS1117-1.5	1.500 V	1.477 – 1.522 V	1.470 – 1.530 V	3.5 V	1.5 %
AMS1117-1.8	1.800 V	1.773 – 1.827 V	1.746 – 1.854 V	3.8 V	1.5 %
AMS1117-2.5	2.500 V	2.462 – 2.538 V	2.450 – 2.550 V	4.5 V	1.5 %
AMS1117-3.3	3.300 V	3.250 – 3.349 V	3.235 – 3.365 V	5.0 V	1.5 %
AMS1117-5.0	5.000 V	4.925 – 5.075 V	4.900 – 5.100 V	7.0 V	1.5 %
AMS1117-ADJ	1.250 V ref	1.231 – 1.268 V	1.225 – 1.275 V	V_OUT+2 V	1.5 %

Datasheet inconsistency worth knowing. The Features bullet on page 1 claims "1.5 % output accuracy" for a list that includes 1.2 V, but the General Description on the same page says 1.2 V is 2 %, and the Electrical Characteristics table settles it: 1.176 – 1.224 V at 25 °C is ±2.0 %, where every other version works out to ±1.5 %. Design to 2 % on the 1.2 V part.

Assets

KiCad symbol, all three footprints and matching 3D models, plus the canonical adom-lbr JSON the rest is generated from.

KiCad symbol	ams1117.kicad_sym (3-pin, all three packages)
KiCad footprints	AMS1117_SOT-223 · AMS1117_TO-252 · AMS1117_SOT-89
3D models	SOT-223 .step / .glb · TO-252 .step / .glb · SOT-89 .step / .glb
Canonical	ams1117.adom-lbr.json
Fusion 360 / EAGLE	Not available yet
Altium	Not available yet

Implementation

Large Automotive Eth Switch Molecule — an AMS1117-1.2 supplies the KSZ9131 gigabit PHY 1.2 V core rail (U902) from the board's 3.3 V rail. 1.2 V is a UMW-only version, so this is a UMW part.
1 A Low-Dropout Regulator AMS — AMS1117 — the original Advanced Monolithic Systems part. Adds 2.85 V and an 8-lead SOIC; drops 1.2 V and SOT-89.

Application notes

Typical circuit is 10 µF in, 22 µF out. The output capacitor is part of the device's stability, not just decoupling. 22 µF tantalum covers every case including a bypassed adjust pin; without adjust-pin bypassing, smaller values work, but the datasheet is explicit that stability degrades as output current rises.
Dropout is load-dependent, and specified all the way to 1 A — 1.20 V max at 100 mA rising to 1.30 V max at the full amp. Size the input rail from the 1 A figure unless the load is genuinely light.
Current limit is high. At 2.1 – 2.5 A this part will happily push well past its 1 A rating into a fault before folding back, so the thermal path, not the current limit, is what protects the board. Thermal shutdown is at 150 °C.
Copper is the heat sink. P_D(max) = (T_J(max) − T_amb) / R_θJA, and the datasheet is clear that R_θJA depends on mounting technique — the 88 / 86 / 102 °C/W figures are a starting point, not a guarantee.
Adjustable output: V_OUT = V_REF × (1 + R2/R1) + I_ADJ × R2, with V_REF = 1.25 V and I_ADJ ≈ 60 µA.

Datasheet

Download the full datasheet (PDF) · UMW (Youtai Semiconductor), AMS1117 1 A LDO Voltage Regulator · umw-ic.com

Provenance

Every electrical number on this page is read from the UMW / Youtai Semiconductor datasheet embedded above — description, features and nomenclature from page 1, absolute maximums and recommended operating conditions from page 2, the Electrical Characteristics table from page 3, pin configuration and function description from page 4, application circuits from page 5, and package outlines from pages 7–8. Nothing from the Advanced Monolithic Systems datasheet is mixed in.
The 2 % accuracy call on the 1.2 V version resolves a contradiction inside the datasheet itself, in favour of the Electrical Characteristics table over the Features bullet. See the note under the version table.
Symbol: generated with adom-symbol to the datasheet's pin description table (1 = GND/ADJ, 2 = VOUT, 3 = VIN).
Footprints: the KiCad 10 official library land patterns, renamed — SOT-223-3_TabPin2, TO-252-3_TabPin2 and SOT-89-3. The TabPin2 variants are correct here because the AMS1117 tab is V_OUT, which is pin 2.
3D models: the matching KiCad 10 official STEP models (SOT-223.step, TO-252-3_TabPin2.step, SOT-89-3.step), converted to GLB with step2glb.
Canonical JSON: ams1117.adom-lbr.json, imported from the KiCad symbol + SOT-223 footprint with adom-lbr import-kicad.
Fusion and Altium libraries are deliberately absent. They are generated rather than hand-verified, and the generated Altium symbol encoding has produced wrong geometry before, so nothing is shipped here until it can be checked in the tool itself.

AMS1117

At a glance

Specifications

Symbol & footprint

Pin map — 3 terminals, identical across all three packages

Internal structure

Component variants

SOT-223-3Lno letter

TO-252-2L CD

SOT-89-3L S

Output voltage versions

Assets

Implementation

Application notes

Datasheet

Provenance

TO-252-2L `CD`

SOT-89-3L `S`